1. Field of the Invention
The present invention relates to an air bag apparatus for a vehicle, and more particularly to an air bag apparatus for a vehicle of a system that senses the air pressure of a tire to determine whether an air bag is operated or not for reliably operating the air bag with respect to accidents of different patterns such as collisions, overturning and headlong falls of vehicles.
2. Description of the Prior Art
Generally, vehicles employ an air bag apparatus for protecting passengers from a shock applied during a car crash. Such an air bag apparatus includes an inflatable air bag, a collision sensor for sensing the collision of the vehicle to generate a collision sensing signal, and an Electronic Control Unit (hereinafter referred to as "ECU") for comparing to analyze the collision sensing signal from the collision sensor to control an operation of the air bag. In addition, the air bag apparatus includes an inflator for injecting a gas or air to the inflatable air bag in accordance with an air bag expansion triggering signal from the ECU for expanding the air bag.
An operation of the conventional air bag apparatus constructed as above will be considered with reference to FIG. 4. First, if a shock is applied to the car body by a collision with another vehicle while running along a road, the collision of the vehicle is monitored by a collision sensor 12 mounted to the forefront of the vehicle. Collision sensor 12 generates a collision sensing signal when the shock against the car body exceeds a preset shock value required for inflating an air bag 62 to supply it to ECU 40 which determines whether the collision sensing signal is received from collision sensor 12 to provide the air bag expansion triggering signal to inflator 64. Once the air bag expansion triggering signal is provided, inflator 64 injects an inert gas such as nitrogen N.sub.2 or argon Ar, or air to inflatable air bag 62 to instantaneously expand air bag 62. Consequently, by the expansion of air bag 62, the passenger in the vehicle can be protected from colliding with a structural part of the vehicle.
Meanwhile, the collision sensor employed for the air bag apparatus has at least one acceleration sensor which measures acceleration/deceleration of the colliding vehicle. Typically, the collision sensor may include a load sensor, a seat belt sensor, and the like in addition to the acceleration sensor. The air bag apparatus for the vehicle having the collision sensor has been disclosed in a plurality of U.S. Patents.
For example, in U.S. Pat. No. 5,246,083 issued to Graf et al., an air bag apparatus is provided with an acceleration sensor for sensing the collision state of a vehicle to generate a collision sensing signal. Here, the acceleration sensor is connected to a pyrotechnic propellant charge for igniting the expansion of the air bag and mounted to the car body at the front of a driver's seat.
In U.S. Pat. No. 5,257,816 issued to Tomiji Sugimoto et al., an air bag apparatus includes acceleration sensors of different kinds which are closely disposed in a single place to constitute an air bag unit, and control the electric current supply to an inflator. The acceleration sensors monitor the colliding moment of the vehicle to generate a collision sensing signal as well as prevent the fault operation of the air bag.
U.S. Pat. No. 5,184,848 issued to Hideo Omura discloses an air bag apparatus provided with a vehicle speed sensor, a load sensor, a seat belt sensor and an atmospheric pressure sensor. Here, the vehicle speed sensor is mounted to a transmission of the vehicle for sensing the moment the car crashes, and the load sensor is to a rear side of a seat for sensing the passenger load to perceive whether the driver is separated from the seat or not. The seat belt sensor is mounted around a buckle of a seat belt for sensing the speed of the passenger colliding against the inflated air bag. The atmospheric pressure sensor is disposed around an air inlet aperture of an engine room hood for measuring the atmospheric pressure to assist an operation of a relief valve associated with a proper expansion force of the air bag.
However, in the conventional air bag apparatus provided with the above sensors, the acceleration sensor or vehicle speed sensor for directly sensing the car crash are only mounted to the forefront portion of the vehicle. Furthermore, the load sensor, seat belt sensor and atmospheric pressure sensor merely serve for assisting the operation of the acceleration sensor or vehicle speed sensor. Thus, if the vehicle is overturned or falls, the sensors fail to operate or normally operate the air bag, so that the passenger is not safely protected from accidents. For example, if the vehicle is partially or completely overturned by as much as 90.degree. to 180.degree. while along on a road, the vehicle temporarily runs along the road surface due to inertia force under the state of being overturned prior to stopping. At this time, the intensity of the shock applied to the vehicle resulting from the overturn is smaller than the shock generally required for operating the air bag, so that the air bag may not be operated.
In addition, the conventional air bag apparatus lacks of a system for previously warning several dangerous circumstances to a driver while driving the vehicle before the occurrence of the accident to obviate disasters such as a collisions, overturning or headlong falls in advance.